Apparatus for deriving low voltages from a high voltage electrical system



Sept. v13, 1966 E H. PovEY ETAL 3,273,051

APPARATUS FOR DERIVING LOW VOLTAGES FROM A HIGH VOLTAGE ELECTRICAL SYSTEM Filed Nov. 19. 1962 2 Sheets-Sheet 1 Sept. 13, 1966 E H, PQVEY ETAL 3,273,051

APPARATUS FOR DERIVING Low VOLTAGES FROM A HIGH VOLTAGE ELECTRICAL SYSTEM 2 Sheets-Sheet 2 Filed Nov. 19, 1962 y. n ff if? f5 y? United States Patent O 3,273,051 APPARATUS FOR DERIVING LOW VOLTAGES FROM A HIGH VOLTAGE ELECTRICAL SYSTEM Edmund H. Povey, Medford, and Chester L. Dawes, Winchester, Mass., assignors to Doble Engineering Company, Belmont, Mass., a corporation of Massachusetts Filed Nov. 19, 1962, Ser. No. 238,590 4 Claims. (Cl. 323-45) This invention relates to high voltage electrical systems and more particularly to yapparatus for deriving low volt-ages for control and metering purposes tha-t are accurately related to the high voltage of interest.

In high voltage alternating current power systems, it is necessary t-o have available low voltages representative of high voltages `for the operation of such instruments as voltmeters, wattmeters, phase meters, synchroscopes and many types of relays. The high voltages cannot be directly used because of insulation limitations in the instrument and because of the danger of electric shock to operating personne-l. Such high voltages are in the order of 10,000 volts or more, while a common voltage for the operation of instruments is 115 volts. The low voltages must have a known ratio and phase relation to the high voltage, however, to enable the correct evaluation of meter readings and to determine the performance of relays.

Potential transformers are available for .reducing the voltage to measurable values, as is well known. However, such 'transformers are extremely expensive are heavy and bulky and so yare difiicult to transport to the location where they are needed, particularly in field measurements, and they are not always available. These disadvantages increase radically with increases in power-system voltages which at the present time operate at voltages as high as 287,000 and 345,000 volts.

Accordingly, `an object of the present invention is to provide a novel and improved apparatus for .providing a low Voltage accurately related in phase and magnitude to the system voltage in high voltage systems for metering and relaying purposes.

A further object is to provide novel and improved apparatus for establishing quickly a low voltage of a readily measurable value; in the magnitude of 100 volts, for example, which has a fixed ratio to a high voltage and is in known phase relation with it, and for maintaining this fixed ratio `and this fixed phase relation irrespective of load fluctuations in the power system or in the low voltage output, so that this established low voltage is available to operate electrical instruments and meters, relays, etc. without its phase relation and its ratio to the high voltage varying as different loads are applied to it.

In accordance with the invention there is provided a low voltage source supplied by a high voltage (above ten thousand volts) through one or more step down transformers so that initially the low voltage source has no definite ratio and phase relation to the high voltage, and owing to the usual `fluctuating loads on the power system the ratio and phase relation of the low voltage source to the high voltage are changing continuously. In the invention there is provided a compensating circuit which in combination with the low voltage source establishes and maintains an output (load) voltage in constant ratio and phase relation to the high voltage so that the output voltage may be used for accurate control and/ or metering purposes irrespective of deviations in the relation of the output of the low voltage source to the high voltage caused, for example by changes of load on the power system. In the preferred embodiment of the invention a low reference voltage accurately related to the high voltage of interest is derived from an impedance device ICC having a known defect angle for which compensattion is made in establishment of the reference voltage. A fixed portion of a low voltage ofthe same frequency as the high voltage of interest is matched to the reference voltage and applied to the input of a linear amplifier having negative feedback between the output and input stages to maintain the desired linearity. The output of the amplifier is inductively coupled to the supply voltage line and is vectorially added to that supply voltage as -a corrective volt-age to produce an output voltage of sufficient power for control and metering purposes that is continuously maintained in accurate relation to the high voltage. This accurately related output voltage is safe, reliable and offers no hazard to personnel or to the operation of the system.

Other objects, features and advantages of the invention will' be seen as the following description of preferred embodiments thereof progresses, in conjunction with the drawings in which:

FIG. 1 is a schematic diagram of a first embodiment of apparatus constructed according to the present invention;

FIG. 2 4is a schematic diagram o-f a modified impedance device and coupling network suitable for use in apparatus constructed according to the invention;

FIGS. 3a and 3b show vector diagrams which illustrate voltage relations in the apparatus shown in FIG. l; and

FIGS. 4, 5 and 6 are schematic diagrams of still further embodiments of apparatus constructed according to the invention.

In FIG. l there is shown a high voltage power line 1 of voltage E, and connected between the line and ground is an impedance device 2 of known power loss or defect angle. In practice such impedance devices are frequently used as coupling capacitors for high voltage transmission lines and as bushings for transformers and oil circuit breakers. The resistor across each section represents the imperfect nature of the capacitor, or its leakage resistance. The low Voltage end of the impedance device, designated in FIGURE 1 by the terminal 3, instead of being connected directly to ground, is connected to ground through the current coil cc of a wattmeter 4, and a high quality capacitor 5. FIGURE 2 Ishows an alternative arrangement in which the low voltage terminalI of the impedance device is connected directly to ground as frequently occurs in practice. Usually a low voltage tap, G shown in FIGURE 2, Iis available and may be made the point of connection of the current coil cc of the Wattmeter 4, the coil, in series with capacitor 5, being disposed in parallel with one or more of the capacitive sections between the tap 3 and ground. The capacitor 5 and the impedance device in series form a capacitive divider in which the voltage across capacitor 5 is nearly in phase with the high voltage and in a fixed magnitude relation to it. The combined impedance of the current coi-'l of the Wattmeter 4and the capacitor 5 in series is so low relative to the impedance of the capacitor sections between the tap 3 and ground, that virtually all the charging current of the impedance device flows through the coil and capacitor. In FIGURES l and 2 a protective gap 6 is connected between the terminal 3 (or 3') and ground to prevent the voltage at this point from accidentally becoming dangerously high.

An attenuating and phase shifting network unit 13 is coupled to the capacitor 5. This unit may be of the same type as that dsei'gnated by 29, 30, 31 in Patent No. 2,922,952 to Povey and Dawes. For any setting of the network, its output voltage E1 bears a constant magnitude and phase relation to the high voltage E.

The low voltage source may be any low voltage circuit or the usual 11S-volt outlet which are supplied by the same transmission system as that of the high voltage E. In FIGURES 1 and 2 the low voltage source is shown as tthe secondary winding 12 of step down transformer with its primary (high voltage) winding 11 connected between the high voltage line 1 and'ground. AAlthough the transformer 10 is shown as a single transformer, it is intended to represent the many transformers of a power system that are generally employed between a high voltage line and a low voltage service, such as wall outlets. The secondary (low voltage) winding 12 is connected to the input terminals of a phase shifter 8. Autotransformer 9 is coupled to the output terminals 7 of 'the phase shifter and is provided with an adjustable tap Ifor adjusting the magnitude of the low voltage supply Es.

The secondary winding 24 of a transformer 23 is connected between the tap of the autotransformer and the output conductor 16. The primary winding 22 is energized by amplifier 19. The voltage produced in the secondary winding acts in conjunction with the supply voltage Es to provide a low output voltage E2 to the load 26. The potential coil pp of wattmeter 4 is connected across the output voltage E2, so that the wattmeter may be used in the determination of the phase and ratio relation between E2 and the high voltage E as set forth in Ithe Doble Patent 2,922,951.

The transformer 23 4together with its primary winding 22 and secondary winding 24 is designed to match the output impedance of the amplifier with the output impedance of the system, although the transformer may be integrally incorporated in the amplifier. A capacitor 25 coupled across the amplifier output terminals 21 neutralizes the magnetizing current of the transformer primary 22 and thus reduces the load on the amplifier. When the amplifier is inactive capacitor 25 provides a path for the current induced in winding 22 by the load current flowing through winding 24. The secondary winding 24 is designed to carry the rated current output of the system which for 50 watts output at 100 volts would be 0.5 ampere. An H. H. Scott amplifier, Model 025045 having a negative feedback between its output and input stages has been found to be satisfactory. It has a pushpull output stage with a secondary winding 24, which is designed for a sixteen ohm load and is coupled to the primary winding 22, and a separate winding for the feedback signal.

In order that output voltage E2 be maintained in fixed ratio and phase relation with the high voltage E, the amplifier must produce in winding 24 the difference voltage between the supply Voltage Es and the desired output voltage E2. To reduce the voltage requirements of the amplifier, the phase shifter and the autotransformer are initially adjusted under some normal system condition until E2 is in the desired ratio and phase relation'to the high voltage E without the aid of the amplifier voltage. The initial adjustment is therefore made with the amplifier input disconnected by opening switch 20. Proper adjustment may be recognized by comparing E2 with some known reference potential such .as can be obtained from the secondary of a potential transformer, or `it may be determined from the reading of the wattmeter as taught in Doble Patent 2,922,951. Autotransformer 9 is adjusted until E2 has the desired ratio to the high voltage E, and phase shifter S is adjusted until the wattmeter reads the loss in the impedance device taking into account the voltage ratio. The initial adjustment makes E2 a temporary reference voltage without the aid of the amplifier voltage.

When a low voltage source is available that does not deviate beyond some reasonable limit in phase and ratio relation with the high voltage E, the phase shifter 8 and autotransformer 9 may not be required. In this case no initial adjustment is made but the voltage requirements of the amplifier will be somewhat greater.

yInorder t0 supply the proper input voltage to the amplifier 'to maintain E2 as the desired. output voltage,

the `following system is used. A voltage e1 representing the high voltage E is obtained from the voltage divider formed by capacitor 5 and impedance device 2. This voltage is varied in phase and magnitude by means of the attenuating and phase shifting network 13 to become the voltage E1 at output terminal of the network. Once adjusted, E1 has a fixed relation to the high voltage E retaining this fixed relation regardless of Iany load changes on the power system, and thus becomes a permanent reference voltage. A voltage e2 representing a fraction of the output voltage E2 is obtained from tap 17 on potentiometer 15, connected between the low voltage wire 16 and ground. Because potentiometer `15 is resistive the voltage e2 is in phase with E2. The magnitude of the voltage e2 is determined by the position of tap 17 which is set to give e2 a magnitude comparable with El. The difference voltage ec between voltage e2 and E1 is applied to the input circuit of the amplifier through switch 20` and is responsive to changes in the relation of the output voltage E2 to the high voltage E.

The system may be put into operation by the following procedure. Switch 20 is closed and the potentiometer tap 17 and the attenuating and phase shifting network 13 are adjusted until the output voltage E2 has the desired ratio to the high voltage E and is in phase with E. The latter condition obtains when the wattmeter reading indicates the loss in the impedance device, taking into account the voltage ratio. This adjustment is similar to that made in the initial procedure, except that it is the attenuating and phase shifting network 13 that is adjusted rather than the autotransformer 9 and the phase shifter 8.

If E2 has been initially adjusted under some temporary system condition to be the desired out-put voltage with switch 20 open, and if switch 20 is closed and E2 then changes, it immediately becomes readjusted to the desired output voltage in accordance with the procedure described above. It then is evident that whenever the system condition returns to that of the initial adjustment, the amplifier input voltage ec must be zero, equivalent to opening switch 20. This condition is a convenient one upon which t0 base an explanation ofthe compensating action of the circuit. If the voltage Es at the output of autotransformer 9 changes with respect to E, due, for example, to a chan-ge in output on transformer 10, the load voltage would also change except for the action of the amplifier. Any change in the relation between E2 and E would cause ec to acquire a finite value, which would be amplified -by the amplifier 19 to produce a voltage in the secondary winding 24. The voltage of winding 24 adds return to zero and the `amplifier would cease to produce' an output voltage. It is possible, however, to use an amplifier of sufficient gain to make the compensation substantially complete for the intended applications.

FIGS. 3a and 3b illustrate with Vector diagrams the general method of operation of the invention. FIGURE 3a shows the vector relations at the completion of the initial adjustment of the system. (For clarity the vectors are not drawn to scale.) The output voltage E2 and the supply voltage Es differ by the Vector IZ where I is the output current and Z is the equivalent impedance looking into the secondary 24 of transformer 23. The supply voltage Es has been adjusted by means of the autotransformer 9 and the phase shifter 8 so that the output voltage E2 is in the correct ratio to E and in phase with it. Under this condition tap 17 and network 13 have been adjusted until e2 and E1 are equal. Potentiometer 15 does not introduce a phase shift between E2 and e2, so now both E2and E1 are in phase with E. Since e2 is equal to El, the input voltage ec to the amplifier is zero, so that the amplifier does not produce a voltage.

Now let the Voltage source at the secondary 12 of transformer change due, for example, to load changes in the power system, or for other causes. This will cause the supply voltage to change from the value Es to E', as shown in FIG. 3b and the current changes from I to I vamperes. Assume that the change of the supply voltage to ES has occurred instantaneously. The instantaneous output voltage then becomes E'2 which is equal to E's minus I'Z, vectorially. The voltage e'2 at the potentiometer tap 17 remains in phase with E2 and in the fixed ratio to it. The voltage input ec to the amplifier is the vector difference between e2 and E1. This causes the amplifier to develop a corrective voltage in the direction of Ec which attempts to restore the output voltage to its original value E2. However, when the terminal voltage reaches some value such as E"2, the Voltage e2, FIGURE 1, becomes e"2 and the input voltage to the amplifier becomes ec as shown in FIGURE 3b. Note that this very small input voltage e"c must cause the amplifier (with the transformer) to develop the relatively large correction voltage Ec. Theoretically com-plete correction cann-ot be attained, for as E2 approaches E2, the input voltage ec to the amplifier approaches zero as a limit. Thus, to obtain close regulation, the amplifier must have a Very high gain.

It will be realized that in actual operation the changes in the vector relations of FIGURE 3b which have just been discussed occur almost instantaneously. Hence, any small departure of the output voltage from its correct value E2 is instantly corrected so that such a radical change to voltage E2 actually would not have opportunity to occur. For example, we have found that with a sudden ch-ange in the supply voltage Es of as much as ten percent the variation in the rea-ding of a voltmeter connected to measure the output voltage E2 is almost imperceptible.

FIGURE 4 shows an embodiment of the invention in which two impedance devices, rather than a single one, are used. One supplies the current to the wattmeter, the current a-cting as a reference when bringing the output voltage E2 into phase with the high voltage E; the second impedance device supplies the low reference Voltage E1 which remains llocked in with the high voltage E. Thus in FIGURE 4, in one respect the impedance device 2 corresponds to impedance device 2 in FIGURE 2 in that either its power loss or power factor must be known. However, the capacitor 5 in FIGURE 2, which is coupled between one current coil terminal c and ground, is omitted. The second impedance device 2 which is similar to device 2 in FIGURE 2 is also connected between the high voltage line 1 and ground. This second impedance device has a low voltage tap 3". Unlike impedance device 2, it is not necessary that its loss or power factor be known, Ibut only necessary that its impedance remain constant. The voltage at tap 3" may be too high to be adapted to the measurement system so that a capacitive voltage divider 27 may be necessary. This consists of two adjustable capacitors c1 and c2 in series. To be able to shift the phase of the voltage at the tap 28 between c1 and c2, c1 is shunted by an adjustable resistor R1 and c2 by an adjustable resistor R2. The capacitive voltage divider 27 performs the same function as the ratio and phase shifting network 13 in FIGURES 1 and 2.

Aside from the fact that the reference voltage is supplied from tap 3 rather than capacitor 5 in FIGURES 1 and 2, the system of FIGURE 4 is equivalent to that of FIGURE 2,. The system is put into operation in precisely the same manner as that of FIGURES 1 and 2. With switch '20 open, the tap at autotransformer 9 is adjusted until E2 has the desired ratio to E and the phase shifter 8 is adjusted until thev wattmeter 4 indicates the power loss in the impedance device 2. E2 is now in the desired ratio to E and in phase with it. The tap 17 is adjusted until e2 has a suitable ratio to E2 and capacitors c1 and c2 together with resistors R1 and R2 are adjusted until E1 is equal to e2 which condition occurs when ec=0. Then E1 becomes a permanent reference voltage. The switch 20 may now be closed and the amplifier operates to maintain E2 in the constant relation to E.

It will be -appreciated by those skilled in the art that if the power factor or the phase angle, rather than the power loss in `the impedance device, are known, the well-known formula W: VI cos 0 may -be used to determine the wattmeter reading, where W is the watts, V the voltage, I the current and 0 the phase angle. Also phase-sensitive devices other than -a wattmeter may be used to establish the reference voltage. The Wattmeter is shown as being a common and readily understood phase-sensitive instrument.

Another embodiment of the invention is illustrated in the diagram of FIGURE 5 in which the initial setting of the desired ratio and the in-phase relation is obtained by bringing the low output voltage E2 into phase with a reference voltage ET which is known to be in phase with the high voltage and preferably in a known ratio to it. Such a reference voltage can be obtained from the secondary of a potential transformer 29 or from -a high voltage measurement device such as is disclosed in Patent No. 2,922,- 952 issued to E. H. Povey and C. L. Dawes.

Much of the diagram of FIGURE 5 is identical with that of FIGURE 4. The portion of the apparatus which includes wattmeter 4 is omitted, and the impedance device 2 has been replaced in FIGURE 5 by a potential transformer 29 having a primary 30 and a secondary 31, and a ratio and phase meter 32. The voltage ET at the transformer secondary 31 which has -a known ratio to E and is in phase with it is called the first reference voltage ET. The voltage divider 27 is identical with the voltage divider 27 in FIGURE 4. The voltage at tap 28, between capacitors c1 and c2 becomes a second reference voltage E1. By means of a double-pole single-throw switch 33, the secondary 31 may be coupled to the output conductor 16 and ground through a ratio and phase meter 32.

The initial adjustment of the system shown in FIG- URE 5 is made with switch 20 opened and switch 33 closed. The tap on autotransformer 9 is then adjusted until E2 is equal in magnitude to ET and the phase shifter 8 is adjusted until E2 is in phase with ET, both of these conditions being indicated by the ratio and phase meter 32. As indicated above, this initial adjustment may not be required if a low voltage source lis available that does not deviate beyond some reasonable limit in phase and ratio relation with the hi-gh Voltage E, in which case phase shifter 8 and autotransformer 9 are not used.

To put the system into operation, switch 20 is closed, and E2 is made equal in magnitude and in phase with ET by adjusting the position of tap 17 and the values of c1, c2, R1 and R2, again using the phase meter 32 to indicate these conditions. The amplifying system then operates to maintain E2 in the correct relation to E. Switch 33 may then be opened and the reference source ET is no longer required.

There may be conditions under which it is desirable to have the output voltage E2 at some angle with E rather than in phase with it. These conditions can occur in a three-phase system in which the phase-to-phase voltage and the voltage to neutral may differ by 30 (or A phase angle such as qb between E2 and E can be readily established by means of this invention. Thus, in the initial adjustment of the systems shown in FIGURES 1, 2 and 4 with switch 20 open, the autotransformer 9 is adjusted until the output voltage E2 has the desired ratio to the high voltage E and the phase shifter 8 is adjusted until the wattmeter indicates that the desired phase angle is attained between the output voltage E2 and the high voltage E. Proper adjustment of the phase shifter is reached when the wattmeter reading equals E21 cos (High) where E2 is the output `voltage applied to the potential coil of the wattmeter, I is the current in the impedance device, 0 is the phase angle of the impedance device and is the phase to be established between E2 and E. If E2 is to lead E, gb is vadded to 6; if E2 is to lag E, qb is subtracted from 9.

In the initial adjustment of the system shown in FIGURE 5, the autotransformer 9 and the phase shifter 8 are adjusted until the output voltage E2 has the desired ratio to the high voltage E, and the desired phase angle qb with E. Both conditions are determined by the reading of the phase and ratio meter 32.

To put the system into operation so that the output voltage E2 is maintained at a desired ratio to the high voltage E, and at a constant phase angle qi with E, switch 20 is closed and the phase shifting network 13 or the capacitive voltage divider 27 is adjusted until E2 has the desired relation. In the systems of FIGURES 1, 2 and 4, the desired phase relation is indicated when the wattmeter reading equals El cos (Hip) which is the same value used for the initial adjustment previously explained. In the system of FIGURE 5, the desired ratio and phase relation is indicated directly by the ratio and phase meter 32.

In the embodiments of this invention such as are shown in FIGURES 1 and 2, the low voltage source from the transformer secondary 12 is shown as being supplied by the same high voltage line that is energized by the high voltage E. However, this arrangement is shown for convenience only, it being intended that the low voltage source be a general one which may be taken from any convenient electric outlet connected anywhere to the high voltage power system. Hence, the phase shifter 8 lmust have a wide range yof adjustment capable of shifting the phase through a range of -lto 180, if necessary, in order to bring the supply voltage Es within the correcting range of the amplifying system. Thus, in FIGURE 3b the correcting range corresponds to the angle where ab is the maximum corrective voltage which the amplifier can develop and b is tangent to the circle at b.

A further embodiment is shown in FIGURE 6 in which the low voltage source is a low voltage tap 37 of an impedance device 34 which may be similar to those Vof the earlier embodiments such as device 2 in FIG- URES 1 and 2. In the operation of electric power systems, power is frequently taken from -such taps, usually reduced in voltage by means of a transformer, for such low v-oltage purposes as the operation of relays. A major disadvantage of such a power source is that the high impedance of that section of the impedance device between the high voltage terminal and the voltage tap makes the regulation of the source very poor in respect to load and the amount of power which may be taken is very limited. In fact, such sources are generally equipped with comp'ensating circuits that may be adjusted to a given fixed load. It is sometimes desirable, however, to 'change the number of relays connected to such a source. By means of this invention, changes in the output voltage if the impedance devic'e due to load changes may be compensated, and a low voltage obtained which will be `constant in phase and magnitude relative to the systems high voltage ove-r a wide range of loads. It is not necessary that the power loss or power factor of device 34 be known. The primary 35 of a step down transformer 36 is coupled to the low voltage tap 37. The output voltage of the transformer secondary 38 becomes the supply Voltage Es and is connected to the load conductor 16 through the secondary 24 of transformer 23. The system is put into operation and thereafter operates in similar manner as that of the embodiment of FIGURE 1. It is obvious that this embodiment is particularly well adapted to this method of operation in that the supply voltage Es is very nearly in phase with the high voltage E.

This last embodiment is advantageous in the fact that the apparatus is much simplified by the elimination of two major elements, the phase shifter 8 and the autotransformer 9, each of which mustbe capable of carrying the entire power output of the system. Moreover, a

phase shifter such as 8 usually involves aixed and rotatable laminated iron structure with windings as well as a 3-phase power supply. On the other hand the network 13 supplies practically no power output and so can be very small, consisting only of very small capacitor and resistor elements.

This invention is highly advantageous in that the amount of the power amplified is very small compared with the power output of the system. For example, the supply voltage would almost never change more than 10%. This would permit a change in phase angle of about 6 degrees (see FIGURE 3b). Thus, if the system operates at 50 watts, 100 volts and 0.5 ampere the amplier need have a capacity of only 10 O.5, or 5 watts, a small proportion of the total power involved. In practice the changes in the supply voltage almost always are very much smaller and the amplifier responds so quickly that changes in the output voltage are almost imperceptible.

Tests were conducted to determine the accuracy of the compensating action. The connections were substantially those of FIGURE 5. The high voltage was held constant at a value of 52,800 yolts and Es was varied deliberately in both magnitude and phase by changing the tap on autotransformer 9and the settin-g rof'phase shifter 8. The amount of variation in Es was measured by connecting a phase and ratio meter between Es and ET. The resulting values -of E2 were then compared in magnitude and phase with ET with the results shown in Table I. The transformer 29 which supplied ET was a high grade potential transformer which held ET substantially at JWO of E and in phase with it. The load current was 0.2 ampere.

It will be noted that even with large changes in the supply voltage Es, the output voltage E2 is held almost yexactly at its correct ratio to E, and the departure in its phase from that of E is very small.

Various such modifications that are within the spirit and scope of the invention will no doubt occur to those skilled in the art, so that the invention should not be deemed to be limited to the details of what has been illustrated and described herein by way of example; but rather it should be -deemed to be limited only by the scope 4of the appended claims.

We claim: Y

1. Apparatus for establishing and maintaining a low output volta-ge in a xed ratio to and in phase with a high voltage comprising a first impedance device of known power characteristics connected to said high Voltage, a low voltage source that provides an output voltage of the 4same frequency as said high voltage and a phase relatively close to that of said high voltage,

first control means coupled to said high voltage including phase `shifting and magnitude adjusting means for providing a first reference voltage in fixed magnitude and phase relation to said high voltage,

second control means coupled to said low voltage source including means for Varying the magnitude and shifting the phase of said output voltage 'for providing a second reference voltage that is a fraction of said output voltage,

a phase sensitive device coupled to said tirst impedance device and to said low voltage source for providing an indication of the phase diiference between said output voltage and the output of said first impedance device `for controlling the adjustment of said first control means to establish said first reference voltage in phase with and in predetermined magnitude relation to said high voltage,

linear amplifying means having an input stage, an output stage, and negative `feedback between said input and output stages,

means vfor applying the difference between said first lreference voltage and said second reference Voltage to said amplifying -means to generate a correction voltage, the power of which is a small fraction of the power of said output voltage,

and a transformer connected between the output of said amplifying means and said second control means for inductively combining said correction voltage with said output voltage in an addition operation to provide and maintain a continually compensated low output voltage in a given fixed ratio to and in phase with said high voltage.

2. The apparatus as claimed in claim 1 wherein the impedance characteristics of `said first impedance device are primarily capacitive.

3. The apparatus as claimed in claim 2 wherein said phase sensitive device is a wattmeter having a first input circuit including a potential coil and a sec-ond input circuit including a current coil, said potential coil being connected to sense said output voltage and said current coil being connected to said first impedance device.

4. The apparatus as claimed in claim 3 wherein said current coil is connected in parallel with a capacitive section of said impedance device and the impedance of said capacitive section is substantially greater than the irnpedance of said current coil so that virtually all the charging current of said impedance device flows through said current coil.

References Cited by the Examiner UNITED STATES PATENTS 2,788,489 4/ 1957 Hollywood. 2,922,951 1/ 1960 Doble. 2,922,952 1/ 1960 Povey et al. 3,011,123 11/1961 Povey. 3,076,134 1/1963 Bennett et a1 323-66 3,098,193 7/1963 Wallace et al. 323-66 3,098,194 7/1963 Clemens 323-66 3,106,686 10/1963 Abrams et al. 323-79 JOHN F. COUCH, Primary Examiner.

LLOYD MCCOLLUM, Examiner.

D. L. RAE, A. D. PELLINEN, Assistant Examiners. 

1. APPARATUS FOR ESTABLISHING AND MAINTAING A LOW OUTPUT VOLTAGE IN A FIXED RATIO TO AND IN PHASE WITH A HIGH VOLTAGE COMPRISING A FIRST IMPEDANCE DEVICE OF KNOWN POWER CHARACTERISTICS CONNECTED TO SAID HIGH VOLTAGE, A LOW VOLTAGE SOURCE THAT PROVIDES AN OUTPUT VOLTAGE OF THE SAME FREQUENCY AS SAID HIGH VOLTAGE AND A PHASE RELATIVELY CLOSE TO THAT OF SAID HIGH VOLTAGE, FIRST CONTROL MEANS COUPLED TO SAID HIGH VOLTAGE INCLUDING PHASE A SHIFING AND MAGNITUDE ADJUSTING MEANS FOR PROVIDING A FIRST REFERENCE VOLTAGE IN FIXED MAGNITUDE AND PHASE RELATION TO SAID HIGH VOLTAGE, SECOND CONTROL MEANS COUPLED TO SAID LOW VOLTAGE SOURCE INCLUDING MEANS FOR VARYING THE MAGNITUDE AND SHIFTING THE PHASE OF SAID OUTPUT VOLTAGE FOR PROVIDING A SECOND REFERENCE VOLTAGE THAT IS A FRACTION OF SAID OUTPUT VOLTAGE, A PHASE SENSITIVE DEVICE COUPLED TO SAID FIRST IMPEDANCE DEVICE AND TO SAID LOW VOLTAGE SOURCE FOR PROVIDING AN INDICATION OF THE PHASE DIFFERENCE BETWEEN SAID OUTPUT VOLTAGE AND THE OUTPUT OF SAID FIRST IMPEDANCE DEVICE FOR CONTROLLING THE ADJUSTMENT OF SAID FIRST CONTROL MEANS TO ESTABLISH SAID FIRST REFERENCE VOLTAGE IN PHASE WITH AND IN PREDETERMINED MAGNITUDE RELATION TO SAID HIGH VOLTAGE, LINEAR AMPLIFYING MEANS HAVING ANINPUT STAGE, AN OUTPUT STAGE, AND NEGATIVE FEEDBACK BETWEEN SAID INPUT AND OUTPUT STAGES, MEANS FOR APPLYING THE DIFFERENCE BETWEEN SAID FIRST REFERENCE VOLTAGE AND SAID SECOND REFERENCE VOLTAGE TO SAID AMPLIFYING MEANS TO GENERATE A CORRECTION VOLTAGE, THE POWER OF WHICH IS A SMALL FRACTION OF THE POWER OF SAID OUTPUT VOLTAGE, AND A TRANSFORMER CONNECTED BETWEEN THE OUTPUT OF SAID AMPLIFYING MEANS AND SAID SECOND CONTROL MEANS FOR INDUCTIVELY COMBINING SAID CORRECTION VOLTAGE WITH SAID OUTPUT VOLTAGE IN AN ADDITION OPERATION TO PROVIDE AND MAINTIAN A CONTINUALLY COMPRNSATED LOW OUTPUT VOLTAGE IN A GIVEN FIXED RATIO TO AND IN PHASE WITH SAID HIGH VOLTAGE. 